1. Field of the Invention
The present invention relates to a photoelectric sensor detecting an object by means of light projection and light reception and, more particularly, to a photoelectric sensor with an increased degree of optical setting freedom as to detection medium light (a projected beam) emitted from a light projection section.
2. Description of the Related Art
Disclosed in JP 2001-264453, A, for example, and others is a long distance type photoelectric sensor for detecting the presence or absence of an object in a production line or the like in a factory. Generally, a photoelectric sensor of this kind is of an amplifier separation type including a sensor head unit and an amplifier unit. As sensor head units, products of various types with different specifications have been available on the market, which are exemplified as follows: a minimum spot reflection type realizing a spot of 50 μm in diameter at a position of 70 mm±15 mm apart forward from a sensor; a linear beam returning type realizing a spot of about 1.5 mm at a position of 1 m apart forward from a sensor to return the light beam to a sensor head through a reflecting mirror; a long distance area reflection type realizing a beam, in the shape in section of a line, and having about 70 mm in area width at a position of 300 mm apart forward from a sensor; and the like.
In order to perform correct object detection in a long distance type photoelectric sensor of this kind, a projected beam, which is a detection medium light, has to be set in an optimum state adapted for a detection object in a particular situation. Various problems have been traditionally pointed out in connection to setting of the projected beam.
A first problem is of an optical axis deflection angle associated with a projected beam. Deflection angles of projected beams in actual products usually range from a good precision within ±2 degrees of a target optical axis to a poor precision within ±5 degrees of a target optical axis. A deflection angle of the optical axis of a projected beam of 2 degrees would result in deviation of the optical axis of 10 mm at a position of 300 mm apart forward from an emission point. A cause for the presence of an optical axis deflection angle is an eccentricity of a light projecting lens relative to a light projecting element (a light source) and, in order to eliminate such a cause, it is required to raise precision requirements for constituent parts of a sensor head to extremities thereof, which cannot be realized in terms of cost. In such circumstances, even with improvement on positioning precision between a sensor head case and a support member in installment of a sensor, difficulty remains in aligning the optical axis of a projected beam in a correct direction since the projected beam originally has an optical axis deflection angle in the sensor head itself. Therefore, when mounting in an actual scene, a necessity arises for angular and positional adjustment mechanisms interposed between the sensor head case and the support member, raising problems of unfavorable cost performance and a cumbersome installment work. Especially, since an optical axis adjustment tolerance in installment of a long distance type photoelectric sensor of this kind is narrow and delicate, it is considerably difficult to realize an angular adjustment mechanism capable of not only freely changing an angle but also fixing a state having adjusted in angle with certainty, and what's worse, in more of cases an inconvenience has been often encountered that optical, axis deviation occurs for the second time due to a clamping stress caused when being screwed in fixing despite of having completed angular adjustment at the expense of time and labor.
A second problem is that a different sensor product have had to be purchased for each case with different geometrical specifications (such as conversing light, diffusing light, slit light or the like) of a project beam so as to match with the geometrical specifications, though there are almost none of fundamental differences with respect to constituent parts in a sensor head case, which is not only a corresponding burden on the side of a user in terms of economy, but also inconveniences on the side of a maker of the sensors because of increase in the number of sensor products adversely affects a production cost and that accompanying complexity in product management leads to a higher production cost.